Daily pill can end HIV epidemic

IT COULD be the end of AIDS as a global epidemic. Antiretroviral drugs that block the spread of HIV are about to transform the battle against AIDS and in theory could even eliminate HIV from some parts of the world. "This is a watershed," says Robert Grant at the University of California in San Francisco. "We can now envision a world where HIV infection becomes rare."

The first approach is called pre-exposure prophylaxis (PrEP). Two independent groups working in Africa have announced that putting uninfected heterosexual people on low doses of ARVs reduced their risk of catching HIV by 63 to 68 per cent - on just one 25 cent pill a day. A constant level of ARVs in the bloodstream kills the virus before it can establish an infection, preventing HIV from taking hold. This worked for both men and women - the hardest group to protect in Africa partly because many are pressurised into having unsafe sex. "[The results are] really exciting, just super," says Catherine Hankins, chief scientific adviser to UNAIDS - the Joint United Nations Programme on HIV and AIDS.

Another major study using "treatment as prevention" (TasP) has had great success in giving ARVs to infected people earlier than usual, before the virus has destroyed many white blood cells. In a trial which covered 13 countries and involved 1763 heterosexual couples, early intervention with ARVs reduced the spread of HIV to uninfected partners by a massive 96 per cent.All the studies were halted early so the placebo groups could get the real treatments.

"We now have a powerful package of preventive measures. We didn't have that a week ago," says Jared Baeten at the University of Washington in Seattle, leader of one of the PrEP studies. This is welcome news since HIV is spreading 2.5 times as fast as people are put on ARVs.

"Now the question is how each country should roll each of these measures out," says Baeten. That is tricky, as it means giving powerful drugs to two new groups, people who are uninfected or have yet to develop symptoms. Advocates of TasP worry that HIV-negative people, who vastly outnumber those with HIV, even in Africa, will consume limited supplies of ARVs that could otherwise be used to treat infected people. Baeten says PrEP should therefore be targeted at high-risk groups - sex-workers, vulnerable young women, uninfected partners of HIV carriers and men who have sex with men.

Drug resistance could be a problem, though. Infected people take three different ARVs to stop the virus becoming resistant; taking just one or two leads to resistance in six months. Uninfected people on PrEP get one or two ARVs, so they must be virus-free. The trouble is the tests are not always accurate: one person on PrEP in the African trials was already infected, and developed resistance.

PrEP is not 100 per cent effective either, especially as healthy people are more likely to forget their medicine than those with symptoms. So people on PrEP must be repeatedly tested, and switched to three-drug treatment if they do become infected, says Grant, who successfully tested PrEP in homosexual couples in the US last year. Long-lasting drugs that do not need to be taken every day are being developed, which could make compliance easier.

Jonathan Weber of Imperial College London, isn't convinced. "I can't see how on earth the benefits of PrEP can outweigh the detrimental aspects," he says. Weber is concerned that PrEP may change sexual behaviours for the worse. Computer models suggest PrEP can increase the spread of HIV if just 15 per cent of users feel protected enough to dispense with condoms.

With TasP, infected people start taking ARVs before their white blood cells fall below 350 per microlitre of blood, while they can still block viral spread; the ARVs then take over by cutting blood levels of HIV. Besides cutting transmission, Myron Cohen at the University of North Carolina at Chapel Hill reported this week that this led to healthier HIV carriers, with fewer cases of tuberculosis The New England Journal of Medicine (DOI: 10.1056/NEJMoa1105243).

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